Hi Matthew ,
I understand your frustration and I hope I can point you to the right direction.
First thing I recommend is checking out this video that talks about Arago.
http://focus.ti.com/docs/training/catalog/events/event.jhtml?sku=OLT113005
Quick Summary:
Arago is a TI distribution that is built on top of OE/Yocto. OE is simply a build framework to create a Linux distribution. Yocto has a distribution, Angstrom is a distribution and Arago are all distributions created via Openembedded. So your comment about a lot of Arago documentation stopping short at starting an initial build is correct since the knowledge you really need is related to Openembedded since those skills are what is used to create distributions.
There are several Openembedded trainings out there that are tailored to generic OE/Yocto so it may not provide something useable on a TI platform since they use a different kernel and u-boot. Meta-ti is the only supported location for BSP software for TI devices so unless your training has you using meta-ti then you will likely have problems getting an image working on a TI board.
I highly recommend that you read through the Getting Started with Openembedded presentation (http://processors.wiki.ti.com/index.php/Sitara_Linux_Training:_Getting_Started_with_Openembedded). Very little concepts are actually specific to SDK 6. The biggest being the config file to use with oe-layersetup. So you would use amsdk-07.00.00.00-config.txt instead of amsdk-06.00.00.00-config.txt. The labs will not work as is but the concepts are still valid and you shouldn't have an issue making the minor tweaks to get it to work on the 7.0 based config. However, that training I believe answers almost all of your questions and helps you get started. It assumes you know nothing about OE so it tries to teach some basic OE skills that are needed to properly navigate the various recipes in meta-arago.